EP1970539A1 - Diffuser assembly - Google Patents

Abstract

The arrangement (1) has a flow acceleration device with a flow guiding device (9) that extends within an outer diffuser (2). The flow acceleration device forms a manifold (11) with its outer surface (10) facing an inner surface (8) of the outer diffuser, and a section of the inner surface of the outer diffuser, where a portion of a boundary layer flow formed on the inner surface of the outer diffuser is acceleratable in a main flow direction in such a manner that a flow separation is stopped on the inner surface of the outer diffuser.

Description

The invention relates to a diffuser arrangement and more particularly to an exhaust steam room of a steam turbine or an exhaust gas space of a gas turbine with the diffuser arrangement.

A diffuser is a fluid-permeable channel which delays the fluid in a transfer-free flow through cross-sectional widening and according to Bernoulli's theorem reduces the kinetic pressure of the fluid in favor of the static pressure.

und dem Gesamt- bzw. Totaldruck p_total,ein, dem statischen Druck pein am Diffusoreintritt und dem statischen Druck p_aus am Diffusoraustritt definiert ist.The quality of the diffuser is described by the pressure recovery coefficient associated with $${\mathrm{C}}_{\mathrm{p}}\mathrm{=}\left({\mathrm{p}}_{\mathrm{out}}\mathrm{-}{\mathrm{p}}_{\mathrm{one}}\right)\mathrm{/}\left({\mathrm{p}}_{\mathrm{total}\mathrm{.}\mathrm{one}}\mathrm{-}{\mathrm{p}}_{\mathrm{one}}\right)$$

and the total or total pressure p _{total, a} , the static pressure pein at the diffuser inlet and the static pressure p _out at the diffuser outlet is defined.

For example, diffusers are used in pipelines for pressure recovery or for continuous bridging of cross-sectional extensions (transitional diffuser). In pipelines with a circular cross section, the diffusers are formed axially symmetrical. In Fig. 4 a longitudinal section of an axisymmetric diffuser 101 is shown and shown schematically the flow occurring typically therein. The diffuser 101 has an inlet cross section 102 and an outlet cross section 103, whose area ratio is greater than one. Upstream of the diffuser 101, a cylindrical inflow pipe is arranged, through which an inflow 108 flows, and downstream of the diffuser 101 a cylindrical outflow pipe is arranged, through which an outflow 109 flows.

Due to the adhesion of the fluid to the diffuser wall, a boundary layer is formed in the near-wall flow. In the lower half of the in Fig. 4 five characteristic velocity profiles 110 to 114 are shown along the main flow direction, wherein the first two velocity profiles 110, 111 show the wall-near flow in the inflow pipe and the upstream three velocity profiles 112 to 114 the wall-near flow in the diffuser 101.

As the flow in the diffuser 101 is retarded, the flow velocity of the main flow decreases in the flow direction, whereby the static pressure of the flow in the flow direction increases correspondingly, satisfying the first law of thermodynamics. According to Prandtl's boundary layer theory, the static pressure in the boundary layer is constant across the flow direction.

Due to the retarding effect of the diffuser 101 and the adhesive condition on the diffuser wall, the flow velocity of the near-wall flow decreases. After overcoming a certain flow path, the gradient of the flow velocity across and against the diffuser wall is zero. This location is a separation point 105 of the flow shown in the boundary layer profile 113.

At the separation point 105, the flow moves away from the diffuser wall toward the center of the diffuser 101, forming a return flow downstream of the separation point 105 near the wall forming a detachment bladder 106. The detachment bladder 106 causes a constriction of the effective cross-section of the diffuser 101, so that the main flow in the region of the detachment bladder 106 is accelerated. As a result, the kinetic energy increases in the main flow and the flow settles in the outlet pipe at a restart point 107 again.

The opening degree of the diffuser 101 largely determines the shape and size of the peel-off bubble 106 and the location of the peel-off point 105 and the optionally occurring reapplication point 107. The higher the opening degree of the diffuser 101, the further upstream the detachment point 105 is.

Due to the narrowing of the effective cross section of the diffuser 101, the peel bladder 106 reduces the pressure recovery effect of the diffuser 101 as compared to a diffuser in which the flow is fully applied.

A steam turbine or a gas turbine is driven at partial, basic and overload. In the construction and design of the steam turbine or gas turbine whose individual components can be optimized geometrically optimized, for example, in terms of efficiency or aerodynamic or thermodynamic effectiveness only in a single operating point. As a result, in other operating points that are not identical to the design operating point, the components can not operate optimally.

This situation also applies to an exhaust steam room of the steam turbine or an exhaust space of the gas turbine. The Abdampfraum or the exhaust gas space is conventionally designed as an axial diffuser.

As a rule, the axial diffuser is optimally designed geometrically with regard to the base load so that the axial diffuser can not be optimally operated with partial and overload.

At the entrance of the axial diffuser there is a lower static pressure than at the outlet with optimal design. By lowering the pressure at the diffuser inlet, which also represents the outlet of the blading, the last blade ring is brought to a higher power output.

The mass flow of the flow flowing through the axial diffuser is smaller in the partial load range than in the base load range, whereby the mean flow velocity in the axial diffuser is higher in the base load range than in the partial load range. As a result, the flow in the axial diffuser in the partial load range tends to be more detachable than the flow which occurs in the axial diffuser at base load.

Thus, the pressure recovery in the axial diffuser at part load is lower compared to the pressure recovery at base load. This has the consequence that at partial load, the turbine power is reduced compared to the turbine power at base load. The influence of an improvement in the pressure recovery of a gas turbine diffuser of c _p = 0.1 was estimated by Farohki to be 0.8% of the turbine output power. This relationship applies analogously to axially flowing steam turbines.

A remedy for this could be a reduction in the degree of opening of the axial diffuser, since this slows down the flow less and thus tends less to detach. However, this lengthens the overall length of the axial diffuser, which adversely increases the overall length of the steam turbine or gas turbine.

The object of the invention is to provide a diffuser arrangement whose pressure recovery is high and whose overall length is small.

Fluid can flow through the diffuser arrangement according to the invention and has an outer diffuser having an inner surface and a flow accelerating device which is set up in such a way that at least part of the boundary layer flow forming on the inner surface of the outer diffuser can be accelerated in the main flow direction, so that a flow separation on the inner surface of the outer diffuser Outside diffusers is prevented.

If the fluid flows through the outer diffuser, it is retarded in the main flow direction, whereby the boundary layer flow which forms on the inner surface of the outer diffuser tends in principle to detach. The detachment would come from a place where the kinetic energy of the flow is zero.

By means of the flow acceleration device according to the invention, at least part of the wall-near flow is accelerated, so that the kinetic energy of the wall-near flow is increased. Thereby, it is prevented that the kinetic energy of the near-wall flow is zero at any location, whereby a flow separation is prevented on the inner surface of the outer diffuser. Thus, the diffuser assembly has a high pressure recovery.

Further, the outer diffuser of the diffuser assembly may have a large degree of opening without flow separation occurring therein. As a result, the outer diffuser and thus the diffuser arrangement has a smaller overall length.

The flow acceleration device preferably has a flow guide which extends within the outer diffuser and with its outer surface facing the inner surface of the outer diffuser and a section of the inner surface of the outer diffuser forms a nozzle channel through which the part of the boundary layer flow can be flowed.

Thus, the flow accelerating means is constituted by the nozzle passage defined by the flow guide in cooperation with the inner wall of the outer diffuser. It is thereby achieved that directly on the inner surface of the outer diffuser the near-wall flow, ie just the flow component with otherwise low kinetic energy, is accelerated. This effectively prevents separation in the diffuser arrangement.

It is preferred that the flow guiding device, with its inner surface facing away from the outer surface, form an inner diffuser, through which the fluid flow can be flowed and thereby retarded in the main flow direction.

Thus, in addition to the nozzle effect in the outer region, the flow-guiding device also has a diffuser effect in the inner region, so that the flow through the diffuser arrangement is greatly delayed. This ensures that the pressure recovery of the diffuser assembly according to the invention is high.

Further, it is preferable that the extent of the flow guide in the main flow direction is in the range of 5% to 40% of the extension in the main flow direction of the outer diffuser.

As a result, the flow-guiding device is arranged completely within the outer diffuser and can be placed exactly at that region on the inner wall of the outer diffuser, at which a detachment of the fluid flow is to be expected. Thus, the flow directing can be targeted to a detachment vulnerable area, whereby an effective suppression of flow separation is achieved and yet the disturbance of the main flow through the flow guide is low.

It is preferred that the outer diffuser and the flow guide are formed axially symmetrical and are arranged concentrically about a common axis of symmetry.

Furthermore, it is preferred that the nozzle channel is formed as an annular channel.

As a result, the diffuser assembly advantageously results as an array of multiple diffusers and a nozzle. This arrangement is formed by a series connection of the three diffusers, namely the region of the outer diffuser upstream of the flow guide, the inner diffuser of the Flow guiding device and the region of the outer diffuser downstream of the flow guide, and a parallel connection of the nozzle channel with the inner diffuser of the flow guide. As a result, a compact, simple and effectively acting subdivision of the outer diffuser is achieved, wherein the diffuser arrangement has a compact design.

Preferably, the flow guide is designed as a straight baffle.

As a result, the baffle is advantageously produced inexpensively.

Alternatively, it is preferred that the flow guide is aerodynamically profiled.

As a result, the flow guide has a low flow resistance.

Furthermore, it is preferred that the flow-guiding device is arranged in the range from 80% to 100% of the channel height (radius) of the outer diffuser.

As a result, the flow-guiding device is advantageously effective in the near-wall flow and thereby placed aerodynamically effective.

Furthermore, the flow-guiding device is preferably arranged in the region of the inlet cross-section of the outer diffuser.

As a result, it is advantageously possible for the inlet flow into the outer diffuser of the flow guiding device to already have an accelerated flow in the boundary layer region, which thus does not tend to detach in the course along the inner surface of the outer diffuser.

Furthermore, it is preferred that the flow-guiding device is mounted pivotably relative to the main flow.

This advantageously achieves that the flow guide can be adjusted individually by pivoting relative to the respective flow conditions within the outer diffuser such that the flow guide is aerodynamically effective.

An evaporation chamber of a steam turbine or an exhaust gas chamber of a gas turbine preferably has the diffuser arrangement according to the invention.

Furthermore, it is preferred that the flow acceleration device is arranged on the inner surface of the outer diffuser in the region of its inlet.

Fig. 1

einen Längsschnitt durch ein erstes Ausführungsbeispiel der Diffusoranordnung,

Fig. 2

einen Längsschnitt durch ein zweites Ausführungsbeispiel der Diffusoranordnung,

Fig. 3

einen Längsschnitt durch ein drittes Ausführungsbeispiel der Diffusoranordnung und

Fig. 4

einen Längsschnitt eines Diffusors mit schematischer Darstellung der Strömungsverhältnisse.

In the following, preferred embodiments of a diffuser arrangement according to the invention will be explained with reference to the attached schematic drawings. It shows:

Fig. 1

a longitudinal section through a first embodiment of the diffuser arrangement,

Fig. 2

a longitudinal section through a second embodiment of the diffuser assembly,

Fig. 3

a longitudinal section through a third embodiment of the diffuser assembly and

Fig. 4

a longitudinal section of a diffuser with a schematic representation of the flow conditions.

Like it out Fig. 1 it can be seen, a diffuser assembly 1 on an outer diffuser 2, which is formed around its axis of symmetry 3 rotationally symmetrical. In a plane perpendicular to the axis of symmetry 3 is an inlet cross-section 4 of the outer diffuser 2, through which an inflow 5 flows into the outer diffuser 2, and in another plane perpendicular to the symmetry axis 3 of the outer diffuser 2 is its outlet cross-section 6, from which an outflow 7 emerges from the outer diffuser 2. Limiting the interior of the outer diffuser 2, this has an inner surface 8.

The outer diffuser 2 is designed as a straight diffuser, i. the inner surface 8 of the outer diffuser 2 forms a truncated cone, the cross-sectional area at the inlet cross-section 4 being smaller than the cross-sectional area at the outlet cross-section 6.

Inside the outer diffuser 2, a flow guide 9 is arranged. The flow guide 9 is formed as a guide plate, which is rotationally symmetrical about the symmetry axis 3 of the outer diffuser 2 arranged concentrically with the outer diffuser 2 forms a truncated cone, which tapers upstream.

The flow guide 9 has on its outer periphery an outer surface 10 which is inclined relative to the inner surface 8 of the outer diffuser 2 such that the annular space cross-section in a plane perpendicular to the symmetry axis 3, which is formed between the flow guide 9 and the outer diffuser 2, in the flow direction downsized.

That is, the outer surface 10 of the flow guide 9 cooperates with an opposite portion of the inner surface 8 of the outer diffuser 8 such that the annular channel, which is located between the flow guide 9 and the outer diffuser 2, forms a nozzle channel 11. Thus, the portion of the inner surface 8 of the outer diffuser 2, which faces the outer surface 10 of the flow guide 9, an inner surface 12 of the nozzle channel 11th

Upstream, the flow guide 9 is bounded by its front edge 13 and downstream of its trailing edge 14. In the area of the front edge 13 of the flow guide 9 to the inner surface 8 of the outer diffuser 2 is an inlet cross section 15 of the nozzle channel 11 and in the region of the trailing edge 14 of the flow guide 9 to the inner surface 8 of the outer diffuser 2 is the outlet cross-section 16 of the nozzle channel 11, wherein the cross-sectional area of the inlet cross section 15 is greater than that Cross sectional area of the outlet cross section 16.

Facing away from the outer surface 10 of the flow-guiding device 9, this has an inner surface 17 which forms an inner diffuser 18. The leading edge 13 of the flow guide 9 is arranged in a plane perpendicular to the symmetry axis 3 and forms an inlet cross section 19 of the inner diffuser 18 and the trailing edge 14 of the flow guide 9 is arranged in a plane perpendicular to the symmetry axis 3 and forms an outlet cross section 20 of the inner diffuser 18, wherein the Inlet section 19 is smaller than the outlet cross-section 20 is.

Out Fig.2 the aerodynamic efficiency of the flow guide 9 can be seen. According to Fig. 2 the flow guide 9 is formed as a profiled annular guide plate.

To illustrate the flow conditions in the diffuser assembly 1 are in Fig. 2 Streamlines 21 in the flow guide 9 and a speed profile 22 upstream of the flow guide 9, a speed profile 23 at the trailing edge 14 of the flow guide 9 and a speed profile 24 shown downstream of the flow guide 9.

The streamlines 21 have a convergent course in the main flow direction, as a result of which the flow acceleration caused by the flow-guiding device 9 is indicated. The wall normal velocity gradient on the inner surface 8 of the outer diffuser 2 is upstream of the flow guide 9 in the velocity profile flatter than the velocity profile 23 at the trailing edge 14 of the flow guide 9, which is shallower than the wall normal velocity gradient of the velocity profile 24 downstream of the flow device 9th

As a result, it is shown that the flow which is conducted by the flow-guiding device 9 through the nozzle channel 11 is accelerated (energized). Thus, the flow guide 9 locally increases the velocity of the flow in the vicinity of the inner surface 12 of the outer diffuser 2. In this case, high-energy flow material from the core flow is directed toward the inner surface 12 of the outer diffuser 2 and thus the boundary layer on the inner surface 12 of the outer diffuser 2 supplied. As a result of this energization, the boundary layer on the inner surface 12 of the outer diffuser 2 can overcome larger positive pressure gradients in the main flow direction without detaching from the inner surface 12 of the outer diffuser 2.

As a result, the outer diffuser 2 reacts more benignly against premature detachment. Thus, by providing the flow guide 9 in the outer diffuser 2, a high pressure recovery of the outer diffuser 2 is achieved.

Fig. 3 shows an exhaust space of a gas turbine, which is formed as the outer diffuser 2. The outer diffuser 2 is arranged downstream of a turbine rotor 25 and continues the outflow emerging from the turbine rotor 25 from the inlet cross section 4 of the outer diffuser 2 to the outlet cross section 6 of the outer diffuser 2 under pressure recovery.

The turbine rotor 25 has a turbine rotor hub 26, which is continued by a cylindrical Außenendiffusornabe 27 with the turbine rotor hub 26.

The turbine rotor 25 has a plurality of turbine rotor blades 28 which at their radial outer ends a Have blade tip 29. The turbine rotor 25 is surrounded by a turbine housing 30. In operation, the turbine rotor 25 rotates about its axis of rotation (not shown) while the turbine housing 30 remains stationary. Therefore, a gap 31 is provided between the turbine rotor blade tip 29 and the turbine housing 30 so that the turbine rotor blade tip 29 does not touch the turbine housing 30 during operation of the turbine rotor 25.

In order to avoid scratching of the blades on the turbine housing 30 and thus damage, a minimum distance as a gap 31, the so-called game between rotor blade 28 and housing 30 is necessary. Through this gap, a portion of the mass flow without power output to flow through the rotor blade 28 and leads to energization of the boundary layer. Depending on the design of this gap 31 with or without sealing, more or less mass flow can flow through. In order to avoid or greatly delay a subsequent detachment of the flow in the diffuser, further energization of the boundary layer by the flow-guiding device 9 is desired.

According to Fig. 3 is provided by arranging the flow guide 9 near the inner surface 8 of the outer diffuser 2 in the region of the inlet cross section of the outer diffuser 4 remedy. The boundary layer disturbed by the leakage flow is accelerated by the flow guide 9 on the inner surface of the outer diffuser 8 in the main flow direction, so that the kinetic energy in this flow area is increased. This ensures that the flow in the outer diffuser 2 does not detach on the inner surface 8 of the outer diffuser 2. Thus, the flow losses in the outer diffuser 2 are low and the pressure gain of the outer diffuser 2 is high.

Claims (12)

Fluid-flowable diffuser arrangement (1) having an outer surface having an outer diffuser (2) and a flow acceleration device (9),
which is set up in such a way
in that at least part of the boundary layer flow which forms on the inner surface (8) of the outer diffuser (2) can be accelerated in the main flow direction,
so that a flow separation on the inner surface (8) of the outer diffuser (2) is prevented. Diffuser assembly (1) according to claim 1,
wherein the flow acceleration device comprises a flow guide (9) which extends inside the outer diffuser (2) and with its outer surface (10) facing the inner surface (8) of the outer diffuser (2) and a portion of the inner surface (8) of the outer diffuser (2). forms a nozzle channel (11) through which the part of the boundary layer flow is flowable. Diffuser assembly (1) according to claim 2,
wherein the flow guide (9) with its outer surface (10) facing away from inner surface (17) forms an inner diffuser (18) through which the fluid flow is flowable and thereby delayable in the main flow direction. Diffuser arrangement (1) according to claim 2 or 3,
wherein in the main flow direction, the extension of the flow guide (9) in the range of 5% to 40% of the extent of the outer diffuser (2). Diffuser arrangement (1) according to one of claims 2 to 4,
wherein the outer diffuser (2) and the flow guide (9) are formed axially symmetrical and are arranged concentrically about a common axis of symmetry (3). Diffuser arrangement (1) according to one of claims 2 to 5,
wherein the nozzle channel (11) is designed as an annular channel. Diffuser arrangement (1) according to one of claims 2 to 6,
wherein the flow guide (9) is formed as a straight baffle or aerodynamically profiled. Diffuser arrangement (1) according to one of claims 2 to 7,
wherein the flow guide (9) in the range of 80% to 100% of the channel height of the outer diffuser (2) is arranged. Diffuser arrangement (1) according to one of claims 2 to 8,
wherein the flow guide (9) in the region of the inlet cross-section (4) of the outer diffuser (2) is arranged. Diffuser arrangement (1) according to one of claims 2 to 9,
wherein the flow guide (9) is pivotally mounted relative to the main flow direction. Abdampfraum a steam turbine,
with a diffuser arrangement (1) according to one of claims 1 to 10. Exhaust gas space of a gas turbine,
with a diffuser arrangement (1) according to one of claims 1 to 10.

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